Traditionally, four-wheel drive (4WD) and all-wheel drive (AWD) vehicles enable transfer of drive torque, produced by an engine and supplied through a gear reducing transmission, to front and rear wheel assemblies. Depending upon the particular vehicle configuration, drive torque can be transferred to both the front and rear wheel assemblies on a full-time basis, part-time basis or “on-demand” basis. A vehicle using an “on-demand” system, normally operates in two-wheel drive (2WD) driving one of the front and rear wheel assemblies and selectively transfers drive torque to the other of the front and rear wheel assemblies in response to vehicle driving conditions.
A transfer case is generally provided for enabling the split of drive torque between the front and rear wheel assemblies. The transfer case includes an input, operably interconnected to an output of the transmission, a first output shaft and a second output shaft, respectively interconnected with the wheel assemblies. A transfer mechanism is provided therein for selectively engaging the first and second output shafts, enabling the transfer of drive torque therebetween. The transfer case must be conveniently packaged within a vehicle underbody, avoiding interference with other vehicle components including drive shafts, exhaust, suspension, vehicle frame and the like. Packaging of the transfer case within a vehicle underbody has become more difficult in recent years, as automakers seek to implement 4WD/AWD systems in smaller vehicle applications.
Traditional transfer mechanisms include first and second transfer gears interconnected by a transfer chain. The transfer gears are respectively interconnected with the first and second output shafts for rotation therewith. As the first output shaft is caused to rotate, thereby rotating the first transfer gear, the transfer chain transfers drive torque to the second output shaft through the second transfer gear.
Transfer mechanisms employing transfer chains retain significant disadvantages. A first disadvantage is the limited configurability. As mentioned above, a recent trend is to provide 4WD/AWD systems in increasingly smaller vehicle applications. Thus, underbody packaging plays an important role. Traditional transfer cases are sometimes difficult to properly package due to the limited configurability of the chain-type transfer mechanisms. A second disadvantage if noise, vibration and harshness (NVH) associated with chain-type transfer mechanisms.
In view of the above, it is desirable in the industry to provide an improved transfer case design. In particular, the improved transfer case design should alleviate the problems associated with traditional transfer cases employing chain-type transfer mechanism and should further enable design flexibility for resolving underbody packaging issues.